While the systems I use are specialized versions of systems from other games, I still like to keep the items involved unique in their appearance and name to some degree. However.. While trying this I've come across something rather odd. For my ranger armor I need to involve hides which are gained from different animals like Cows etc. So then I started to think o no I'll need to make unique hides and animals and then monsters.

So basically, do I really need to include unique monsters are do people enjoy the regulars like Skeletons, Dragons, Wolves etc?

Do they want unique monsters? Of course. Are unique monsters a feature they can't live without? Probably not. The question is how important you think this feature is compared to other features you can spend your time working on. I'd say you could probably get by recoloring the icon.

Yeah, but that leaves a lot of room for error, and it's a lot of work for a small feature.

If a user requires you to make some special graphics for a 2d top-down RPG... they have no damned business playing any video game. The graphics do not mean a thing, I promise you. If the function of the item is all the same, I wouldn't care if you put tiny little dog droppings, or green cards, or bear traps... yeah, show me a character wearing a bear trap as a shirt >.>; the point is, the graphics aren't the objective in the game. It's the playability and replayability. If the game is no fun, it's no fun, no matter what you put into it. So far, from what I've seen of your posts... don't worry about what you put in there. Make a basic icon for now, and when you feel like it's not as much of a burden to make every goddamn icon for every goddamn item, which I know can be very tedious (especially coming from the perspective of trying to build a card game, myself... *shoots self in the head*), and when it's not a chore, it's fun to make the icons... only then should you make them. Make them when it's not so much of a burden.

For example. Right now, I'm working on a basic script for a pokemon game. Having trouble getting the pokemon to show up in a statpanel. Know what I'm using as icons for the pokemon? Mouse-drawn numbers 1, 2, and 3. Know why? The graphics don't mean a thing right now.
When the feature is new, the graphics won't mean a thing. Look at just about any Perfect World private server. The graphics are nothing compared to the official server, International, yet, thousands of people play the privies. Why? It's more fun. We don't give a shit about the graphics. We don't care that one mob looks no different than another sans a slight color change. Know what that mob's gonna' look like in a sec?
Dead.
Either it or me, right? heh. Well, I hope I helped and didn't bore too much :\